el7566 Intersil Corporation, el7566 Datasheet - Page 11

• Manufacturer Part Number: el7566
• Description: Monolithic 6a Dc/dc Step-down Regulator
• Manufacturer: Intersil Corporation

The V
temperature. Equation 3 illustrates the relationship and can
be used to accurately evaluate thermal design points.
Full Start-Up Control
The EL7566 offers full start-up control. The core of this
control is a start-up comparator in front of the main PWM
controller. The STP and STN are the inputs to the
comparator, whose HI output forces the PWM comparator to
skip switching cycles. The user can choose any of the
following control configurations:
ADJUSTABLE SOFT-START
In this configuration, the ramp-up time is adjustable to any
time longer than the building soft-start time of 2ms. The
approximate ramp-up time, T
CASCADE START-UP
In this configuration, EN pin of Regulator 2 is connected to
the PG pin of Regulator 1 (Figure 22). V
after V
T
T
V
J
ST
O
V
O2
=
=
75
TJ
O1
RC
+
pin reports a voltage proportional to the junction
is good.
1.2 V
------------------------
⎛
⎜
⎝
0.00384
---------
V
V
FIGURE 21. ADJUSTABLE START-UP
IN
O
–
FIGURE 22. CASCADE START-UP
⎞
⎟
⎠
EL7566
TJ
EL7566
+
-
EN
STN
STP
V
O1
11
ST
R
200K
, is:
C
V
IN
0.1µF
V
V
O2
O1
O2
EL7566
will only start
T
ST
PG
V
IN
V
O
EL7566
LINEAR START-UP
In the linear start-up tracking configuration, the regulator with
lower output voltage, V
voltage, V
OFFSET START-UP
Compared with the cascade start-up, this configuration
allows Regulator 2 to begin the start-up process when V
reaches a particular value of V
goes HI, where V
V
Component Selection
INPUT CAPACITOR
The main functions of the input capacitor(s) are to maintain
the input voltage steady and to filter out the pulse current
passing through the upper switch. The root-mean-square
value of this current is:
for a wide range of V
For long-term reliability, the input capacitor or combination of
capacitors must have the current rating higher than I
Use X5R or X7R type ceramic capacitors, or SPCAP or
POSCAP types of Polymer capacitors for their high current
handling capability.
V
V
I
IN,RMS
REF
O2
O2
=1.26.
=
FIGURE 24. OFFSET START-UP TRACKING
FIGURE 23. LINEAR START-UP TRACKING
O1
-----------------------------------------------
V
V
.
EL7566
REF
O
EL7566
×
(
V
REF
V
+
-
IN
IN
+
-
IN
–
is the regulator reference voltage.
O2
V
V
and V
IN
O
, tracks the one with higher output
V
V
)
O1
IN
×
V
R
REF
I
O
O
A
REF
.
≈
R
(1+R
V
1/2
B
O1
*(1+R
B
I (
/R
V
V
V
V
O
O1
O2
A
O1
O2
)
)
EL7566
B
/R
A
+
) before PG
-
EL7566
STN
STP
May 8, 2006
IN,RMS
FN7102.7
R
O1
C
V
V
IN
IN
.